The present invention relates to sodium conductors and more particularly to sodium-filled flexible transmission cable in which the outer container is a flexible corrugated copper casing filled with the sodium. One of the major problems which arises in the construction and utilization of such cables is the differential in the coefficient of expansion between the sodium on the one hand and the copper on the other hand. Sodium sustains 4% volume change from room temperature through its melting point. In casting a sodium cable in a fixed or corrugated metal tube it has been observed that uncontrolled voids have been formed in the sodium on cooling. This may produce a conductor which could develop undesired hot spots.
Another problem arising from this 4% volume change occurs where a solid sodium conductor is cast in a fixed or corrugated or other flexible metal tube. Extremely large hydrostatic forces may rupture the enclosure. Even if the enclosure is made compliant, the large differential expansion between the sodium conductor and its support system may cause breakage or unacceptable distortion as, for instance, snaking of the conductor or parts thereof.